Biphenyl derived Schiff-base vanadium(v) complexes with pendant OH-groups—structure, characterization and hydrogen peroxide mediated sulfide oxygenation

Abstract

A series of mononuclear oxovanadium(v) complexes of tridentate Schiff bases HL(1)-HL(4) and H(2)L(5)-H(2)L(8) derived from 6-phenylsalicylaldehyde and 6-(2-hydroxyphenyl)salicylaldehyde and four different amines was synthesized. The systematically selected ligands contain aliphatic or aromatic nitrogen, or alkoxy- and phenoxy-oxygen as third donor atom. The complexes were characterised by spectroscopic methods in solution and the solid state. Single-crystal X-ray analyses were performed with VO(2)L(1)(), VO(2)L(3)x1/2EtOH (), VO(2)L(4)(), VO(OiPr)L(7)xiPrOH, VO(OiPr)L(8) and H(2)L(8). For all compounds the vanadium(v) cores contain distorted tetragonal pyramidal geometry around the dioxo- and oxovanadium site at which the N(2)O- and NO(2)-donor ligands bind equatorially. Complexes and display intramolecular hydrogen bonding of the pendant hydroxyphenyl group to a coordinated oxygen trans to a nitrogen atom and therefore serve as suitable models for the native site of vanadium dependent haloperoxidases. Variable-temperature (1)H NMR spectra revealed significant hydrogen bond interaction in acetonitrile solution. In situ prepared catalysts are active for hydrogen peroxide mediated oxygenation of ethyl phenyl sulfide and showed complete conversion of the substrate to ethyl phenyl sulfoxide, together with small amounts of the corresponding sulfone, as detected by GC/MS after 10 min. The complex of H(2)L(7) turned out to be most efficient while HL(1) and HL(2) were completely inactive. Catalysis is supported by the pendant OH group in the complex of HL(3), the catalyst is twice as active as the complex of HL(4).

Mechanistic Analysis of Nucleophilic Substrates Oxidation by Functional Models of Vanadium‐Dependent Haloperoxidases: A Density Functional Theory Study

“…This study was later expanded to determine the factors controlling the stereoselectivity of disulfide oxidation using QM/MM methods [31] on sterically hindered Schiff bases often employed in vanadium catalysis literature. [7,[9][10][11]32] Balcells et. al demonstrated the characteristics of an S N 2-like transition state, where oxido-transfer occurs from the unprotonated oxygen of the peroxido moiety to organic sulfides.…”

Biphenyl derived oxovanadium(IV) and copper(II) salen-type complexes – structure and redox tuning

“…Steric effects of the hydrogen-bonded hydroxygroups may be responsible for the better discrimination of sulfide and the more bulky sulfoxide. Compared with our previously reported peroxide mediated sulfide oxygenation catalyzed by tridentate Schiff base vanadium complexes, the presented salen-type complexes are less active [19]. For the tetradentate complexes studied herein, a cis side-on coordination of peroxide is sterically disfavored and the oxygenation reaction might follow an alternative, less effective pathway.…”

“…These complexes reveal intramolecular hydrogen bonding between noncoordinating hydroxyl groups and coordinated phenolate oxygen atoms. Improved activity of functionalized complexes compared to their unfunctionalized analogs has been observed for the oxygenation of sulfides [19]. Here we expand the study of the effect of second sphere hydroxyl groups on salen-type vanadium complexes which have been widely used in catalysis [20][21][22].…”

N,N:N′,N′-Bis(2,2'-dihydroxybiphenyl-3,3'-dimethylidene)benzene-1,2-diamine dimethyl sulfoxide tetrasolvate

“…Our ongoing studies of the coordination chemistry of macrocyclic ligands (Ku È hn et al, 2001) and metal±functional group co-operation (Ko È vari & Kra È mer, 1996;Plitt et al, 2004) require the synthesis and modelling of known and novel cyclic compounds. The Schiff base macrocycle in the title compound, (I), attracts attention since it might be considered as a dimeric CÐC-coupled form of the well described ligand N,N H -bis-(salicylidene)benzene-1,2-diamine (salphen).…”